TROPICAL NATUEE 



increasing complexity the outward mimicry which now so 

 amazes us. During the long ages in which this process has 

 been going on, and the Danaidae have been acquiring those 

 specialities of colour which aid in their preservation, many a 

 Leptalis may have become extinct from not varying suffi- 

 ciently in the right direction and at the right time to keep 

 up a protective resemblance to its neighbour ; and this well 

 accords with the comparatively small number of cases of true 

 mimicry, as compared with the frequency of those protective 

 resemblances to vegetable or inorganic objects whose forms 

 are less definite and colours less changeable. About a dozen 

 other genera of butterflies and moths mimic the Danaidse in 

 various parts of the world, and exactly the same explanation 

 will apply to all of them. They represent those species of 

 each group which, at the time when the Danaidse first 

 acquired their protective secretions, happened outwardly to 

 resemble some of them, and which have, by concurrent varia- 

 tion aided by a rigid selection, been able to keep up that 

 resemblance to the present day. l 



Theory of Sexual Colours 



In Mr. Darwin's celebrated work, The Descent of Man and 

 Selection in Relation to Sex, he has treated of sexual colour in 

 combination with other sexual characters, and has arrived at 

 the conclusion that all or almost all the colours of the higher 

 animals (including among these insects and all vertebrates) 

 are due to voluntary or conscious sexual selection ; and that 

 diversity of colour in the sexes is due, primarily, to the trans- 

 mission of colour-variations either to one sex only or to both 

 sexes, the difference depending on some unknown law, and 

 not being due to natural selection. 



I have long held this portion of Mr. Darwin's theory to be 

 erroneous, and have argued that the primary cause of sexual 

 diversity of colour was the need of protection, repressing in 



1 For fuller information on this subject the reader should consult Mr. 

 Bates' original paper, "Contributions to an Insect -fauna of the Amazon 

 Valley," in Transactions of the Linnean Society, vol. xxiii. p. 495 ; Mr. 

 Trimen's paper in vol. xxvi. p. 497 ; the author's essay on "Mimicry," etc., 

 already referred to ; and, in the absence of collections of butterflies, the plates 

 of Heliconidae and Leptalidse, in Hewitson's Exotic Butterflies ; and Felder's 

 Voyage of the " Novara," may be examined. 



